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Can a passenger jet be towed to safety if it breaks down in midair?
A car can be towed by a tow truck to the repair shop when it breaks down on the highway. Is it possible for a passenger plane to be towed by an emergency tow plane along the air corridor to the next nearest airport assuming it cannot reach there on its own power (example if it runs out of fuel or both pilots are incapacitated)?
Update:
This question actually consist of two parts. Whether it is feasible and whether this is practical. I have seen a small tugboat towing a barge; a man pulling a firetruck. Before writing off this idea completely, can someone address what's stopping a fighter plane from towing a passenger jet if a proper point of harness is installed?

The plane can't very much wait for the tow like a car. In actual fact, it can still fly/glide for some time and that's how you have a chance to bring to safety. Either that or it's going to crash quickly, making the question moot. If all passengers are incapacitated, other planes can only watch it crash or, conceivably, shoot it down.

Note the difficulty of trying to tow a car before it stops.

If both pilots are incapacitated who is gonna call in for the Tow??? for the moment if a plane runs out of fuel or both pilots are incapacitated in midair there's one thing you can do. Pray

@Tasos: Surely if you can create a means to actually tow a passenger jet, you can create a means to determine if it's needed. Perhaps a deadman switch, a cockpit video stream to ATC, or it just happens automatically if the plane strays too far from its flight plan and nobody responds.

@Gabe -- sure i agree. how about an Artificial intelligence computer on the plane where it lands by itself before it runs out fuel or the pilots are incapacitated. that could work. I don't know about towing though. you will need a tractor beam for that.

This isn't very close, but still ...http://en.wikipedia.org/wiki/Pardo's_Push

They don't come any closer than that. @User58220 If the question was "could the passenger make it to safety being towed in a jet" the answer was, yes.

In the Korean war there was a fighter jet that pushed another fighter jet back to friendly territory after an engine failure over enemy territory. They were equal size aircraft and had helpful nose and tail shapes.

Towing is quite feasible, and even landing while in tow is possible - I've done it myself in gliders. The hard part is catching up with the stricken plane.
To stay with Keegan's Boeing 777: It most likely will travel at Mach 0.8 and somewhere between 30.000 and 39.000 ft when disaster strikes. Let's further assume that power fails instantly, so the aircraft, traveling at 240 m/s, will develop a sink rate of 15 m/s just to continue flying. When it sinks, the increasing density allows it to slow down, so at sea level it will fly at 130 m/s, sinking with 8.125 m/s. For simplicity, assume a linearly decreasing sink rate, and the remaining time aloft will be less than 1000 sec or around a quarter of an hour.
Now the towplane has 15 min to scramble the crew, run up the engines, get take-off clearance and to actually fly an intercept to the stricken airliner. How realistic is that? How many airports are needed to have 777-sized towplanes ready, and how many otherwise unproductive 777s would this scheme need?
A car can stop and wait a couple of hours for the tow to reach it. An aircraft can not.

Finally a sensible answer.

remember that that glider is designed to have far better glide characteristics than that 777, making towing it less feasible. You'd need an aircraft far more powerful than a 777 to tow a 777. Maybe a B-52 could pull it off, or an An-225.

(+1) Good points, especially the fact that aircrafts can't wait in place for a tow, a point that ought to be mentioned. But the question also mentions an incapacitated crew beside engine failure. It's obviously impossible to tow an airliner in this context but the question does not seem entirely absurd,  as there have been cases in which fighter jets made contact.

15 minutes is possibly slightly pessimistic: Air Transat 236 was aloft for 19 minutes after the second engine flamed out and could have gone a little longer if they hadn't been deliberately losing altitude to land at Lajes. But this makes no practical difference: even 20-25 minutes wouldn't give enough time for a rescue.

Also, imagine the cost of needing tow-planes ready in enough locations to reach airliners - astronomical when the number of times they are needed are maybe once a decade.

What is also unrealistic is the expectation that the pilots of the aircraft without power would be able to control things well enough to link up.

Remember please that the 777 carries an ETOPS-180 rating.  That means on over-water flights it can be 180 minutes (3 hours) flying time from the nearest suitable airport.  Some of these planes may be able to fly an ETOPS-240 (240 minutes, or 4 hours) as well.  When they are in fact that far away from the nearest suitable airport, the plan of a tow plane rendezvous in the 30 minutes or less that the disabled airliner has available before impacting the ground/water is just not going to happen.

There are a number of other major problems with such a scheme. Where would you attach a tow cable to on a jetliner? Gliders have specialized attachments. What would you use as a tow plane? A Piper Cub isn't going to cut it, and larger planes don't have towline attachments. How are you going to make the attachment? Gliders are always hooked up on the ground. Are you going to climb outside and tie it on? And finally, you have to look at the number of cases where being able to tow a plane midair would have made a difference to the outcome of a situation. I can't think of any.

@DavidRicherby: My calculation assumed MTOW, and a lighter aircraft will take longer to glide. Your 20 min are a better estimate, but as you said, this does not make a practical difference.

@DJClayworth Your other objections are spot-on but objecting that there are currently no "tow-truck" planes doesn't make sense. Obviously, if such a system were invented, you'd need to attach some kind of device to planes to allow them to be towed and also equip or build a number of "tow-truck" planes. The mere fact that there are no such planes now (because the system hasn't been invented yet!) is no barrier per se to them existing in the future.

Assuming the invention of a "tow truck" plane, which had a means to automatically engage a disabled aircraft and take over its controls (assuming the pilot is incapacitated, you need to lower landing gear, set flaps, etc.), how long would the tow rope have to be? I'd have to imagine that the wake turbulence from any plane capable of catching up to a 777 and towing it would have to be substantial enough that you'd need a mile or more of rope to prevent the towed plane from losing control from flying in the tower's wake.

"I've done it myself in gliders" ??? in mid flight?? you got towed?  (just out of interest, im going to email Nasa and see if its possible) they are working on a tractor beam but for space

@Tasos: Come on, that was not so hard to understand, was it? Landing the glider first does the trick, don't stay in ground effect when the towplane touches down. Then release the tow cable and steer clear of the tow plane. It's really easy.

What about a fighter jet? They could reach the plane much faster. In Japan they tow cars with motorbikes, it's the same concept.

@Nick: No, it is not the same concept unless the motorbike picks up the tow while the disabled car is coasting at 60mph (~100kph).

I think this answer, like many others, assume a scenario where the plane fails, then a tow plan is come up with. Maybe a more realistic situation where this might work is one where we know the plane is going to fail in the future. For example, if there is a fuel leak, and the plane is flying over a rainforest and so unable to land safely. With still potentially hours to go until failure, maybe a rendezvous can be arranged? The towplane doesn't have to land with the jet, only extend its glide long enough to reach safety, then detach.

@SkipMiller Actually, the B777-300ER, -200LR, and -200ER with GE90s are rated for a whooping 330 minutes ETOPS. IIRC, this is the longest ETOPS rating of any aircraft in service.

"The hard part is catching up with the stricken plane." Well, specifically, the hard part is catching up to the plane with something that has sufficient power to tow it. Fighters can and do catch up to planes in flight relatively frequently, but, powerful as they may be, towing a 777 would be a tall order for any fighter. It would probably take 2 or 3 of them working together. The other hard part is then hooking up the tow mid-air. Assuming the towed aircraft was still controllable, they could tow it into a position near enough to an airfield, then release and let it glide in.

Interestingly, the stricken plane may have enough time to glide to the towplane's airport!

I am picturing something like a 777 being towed due to a complete engine failure.  Please correct me if you had something else in mind.
This is unheard of, but it would be possible, and is a very interesting thought.
The first thing that comes to mind is something like a C-17 being refueled by a KC-135

Of course, a loaded 777 will weigh more carrying passengers than a C-17 loaded with cargo, but these mid-air refueling operations, logistically, are not much different that what would be needed to tow an airborne plane.
Here are the differences I can think of - whether or not they are feasible, I'm not sure.

Logistically: the air force has their rendezvous planned down to a couple seconds before the plane that needs fueling is even airborne.  In an emergency situation everything from planning to execution would have to happen in a VERY small amount of time.
When refueling, no major tension is put on the refueling hose.  If a 777 were being towed the tension would be AT LEAST the amount of air resistance acting on the 777.
Designing a hook that can bear the huge forces and moments involved would take a lot of work.

I did a little math to calculate the forward force that would be required to pull a (fully loaded) 777 to keep it above stall speed.
You would need about 43,000lbs - which is not too much in the world of airliners. For example, the 777 has a take off weight of 660,000lbs - and each engine produces over 100,000lbs of thrust.  So it would be very easy to have a well equipped aircraft or two to tow a 777 - once connected.
The total force in the rope, assuming the towing airplane is slightly above the airplane being towed would simply be 42,500lb/cos(angle) so if the length of the rope is a generous 300ft and the towing airplane is 50ft above the towed aircraft, then the total force would be 43,100lb.

Just in case people don't trust my numbers, here's a screenshot of the math.  I had a 777 model on my computer that I used to get the data from:

Quite an interesting discussion has emerged surrounding this answer, but it's a bit much to keep in comments. I've migrated that discussion to chat.

Thanks for doing the maths. I believe that you have forgotten to plug in the drag coefficient Cd when calculating the drag force. Also, a Cd of 0.2 is quite high for a streamline aircraft. I suspect the towing force to be much lower than what you have calculated.

A Cd of 0.02 is more likely. That gives $0.020.50.77770.5^2100 = 3861.88$

Wouldn't the force required to tow a 777 be exactly equal to the force that it's engines would normally produce in level flight?

@reirab:  That would be true only if you towed the 777 at its usual cruising speed.  Towing it more slowly would reduce the force required, unless the speed dropped low enough to put the 777 "behind the power curve".

But it would still be whatever amount of force the engines would normally have to produce to maintain said speed for the same configuration and altitude.

The calculation given appears roughly correct for the average case, but you'll need to design the system for the peak load. Think about a bit of turbulence, slack hitting the line, and suddenly a jerk. Part of this is caught because the rope isn't going to be straight anyway, but cirved under its own weight. The angle part is misleading because you'll have an upward force proportional to sin(angle) which means the towed plane doesn't need the ordinary amount of lift, and that in turns means less drag.

If both pilots are incapacitated, towing the plane is moot because it won't be able to land.
In the case of fuel starvation, an airliner that loses its engines at cruise altitude can glide for maybe 20–25 minutes before it descends to sea level. If there was an airport close enough to scramble a rescue plane from, then the broken plane would have a decent chance of just gliding to a landing at that airport.

+1 because this is a very valid point. If only the airplane is disabled, it would be much quicker/simpler/safer to land it than to scramble something up to pull it around; and if the crew is incapacitated - unfortunately even if you could scramble something up that quickly - it would not be of much use.

There have actually been several incidents of pilots becoming incapacitated and, indeed, fighters can intercept them pretty quickly. For a recent example, there was a TBM 900 that was flying from Rochester, NY to Naples, FL where the pilots became incapacitated. They were intercepted by fighters and escorted all the way to Jamaica before they presumably ran out of fuel and crashed. In this particular incident, if the interceptors had been able to pull the TBM down to a lower altitude, the pilot might have regained consciousness, but that would be really hard to do without his help.

@reirab Scrambling a fighter to attend an unresponsive light aircraft is hardly the same thing as scrambling something capable of towing an airliner.

Very true. I mentioned as much in one of my comments on another answer. The only I way I could think of to do it with something the size of an airliner would be with multiple fighters, preferably attaching somewhere around the engine pylons (since that's where the aircraft is designed to be pulled from anyway.) That would be really hard to pull off, though. Having said that, the last sentence of your answer is not quite true. Even if the interceptor only flew at the same speed as the airliner, they could meet halfway from the field, doubling the potential range.

Its not unheard of - gliders are often carried up by tow planes. However, hitching up a plane on the ground and towing it up is completely different than trying to do the following:

Catching up to a plane flying at great speed.
Positioning yourself in front of it.
Hooking up a tow hook.
Pulling it fast enough to maintain flight.

Suppose you were somehow able to do the first 4, you are still left with the small point of having to land two aircraft that are tied to each other.
So its is nearly impossible to do what you are suggesting.
An airplane will maintain flight as long as there is sufficient lift on the wings.
To tow a disabled plane is really not required, because even if all engines fail (a highly unlikely event), there are contingencies in place to power the control surfaces and communications so that the pilot can glide the plane to a safe landing. See this question for examples of incidents where all power was lost.
Lets assume that everyone on board becomes incapacitated. In this scenario (which has happened before) the plane will continue on its programmed flight path until it runs out of fuel, at which point it will drop in altitude eventually until it crashes.
In April 2012 the pilot of a Cessna 421 was incapacitated (possibly due to hypoxia - lack of oxygen) - the aircraft continued on its programmed course until it eventually ran out of fuel (flightaware flight track):

September 10 had another similar incident.

Good answer, but I think that most of the items in your list are actually very feasible.

I highly doubt it - just thinking off the top of my head what the power requirements would be to do such a thing - I don't know of any aircraft that has the capability.

@BurhanKhalid not an aircraft of comparable size, but you could have something like a C-130 tow a C172. Probably not what OP has in mind as most such questions come from people who think of airliners when thinking aircraft and little else.

(+1) The most famous crew-incapacitated/flight-runs-its-course accident must be Helios Airways Flight 522. Fighter jets were able to reach the plane and escort it for over half an hour so asking whether something else could be done in this situation is not an entirely absurd question.

You wouldn't have to land the two planes tied together. The tow could be released shortly before the landing airport to allow the disabled plane to glide in. Of course, they'd have to land it first time but I doubt you'd be able to do a go-around while towing a large jet anyway.

The simple answer is that it's presently not possible, certainly not for large passenger jets.
That said, it's possible to do rather impressive things like towing a glider or setting up a rendez-vous in mid-air for refueling. Towing would therefore not seem completely out of the realms of possibilities and Keegan's calculations suggest it would even theoretically be plausible (I didn't try to verify the calculations and I am probably not knowledgeable enough to do so).
One problem is that if all engines fail, staying put and waiting for a tow is not an option. Fortunately, planes do not “fall off the sky” either, they can glide in a controlled fashion and that's the actual contingency plan. It has happened before, perhaps most famously to the Gimli glider.
As Pieter Kämpf explained, an additional problem in this situation is that, while it's possible to fly the plane to safety, there is not much time available. Imagining a tow plane is one thing, but having one at the ready to reach a specific point anywhere in the world in 10-20 min is something else entirely and would be prohibitively expensive.
Now, if the pilots are incapacitated, things are quite different. Modern planes can maintain speed and altitude and basically continue to fly. This has also happened before, e.g. to Helios Airways Flight 522 and in that particular case there was more than enough time for fighter jets to reach the distressed airliner and escort it for over half an hour. Ultimately, however, they couldn't do anything else than watch it run out of fuel and crash.
The problem is that “towing” in some way or other is neither needed nor helpful. After all the plane is still entirely capable of flying on her own. What you need is taking control and that's presently not possible either. To my (non-expert) eyes, adding some remote control functionalities seems perfectly doable with current technology (cf. drones) but that would mean adding additional complexity, potential for failure, etc. I assume the cost/benefit analysis does not justify it and, as far as I know, there is no commercial passenger plane with anything like that.

Imagine what the "bad guys" would be able to use such a remote control setup for. Who gets to override the override?

@MichaelKjörling Yes, exactly, that would be one of the potential failures of the system. Thanks for the link!

@MichaelKjorling presumably the pilot can override the override, if he or she is not incapacitated.

Cars and passenger aircraft are designed and maintained in very different ways.
Redundancy
Cars only have one engine, unlike almost the aircraft that carry most passengers. Cars cannot continue their journey if their only engine breaks down or if an axle breaks. Aircraft have multiple independent sets of many of the most critical parts like engines and flight control systems, they are specifically designed to be able to continue when many things break down. An aircraft can continue when one engine breaks down, it can still be flown and make a landing when all engines have broken down. Aircraft have redundant systems to allow for continued operation after multiple failures.
Maintenance and monitoring
Cars might only be looked at by a qualified mechanic once a year or once every 18 months. Even at this time, it is likely that they mechanic just changes the oil in the engine, checks the fluid levels and brake wear and does a few other basic checks specified by the manufacturer. They don't check everything in the car.
An aircraft is more likely to be monitored continuously. It is not unusual for the engines to be sending data to the engine-makers in flight so that the engine makers can measure the health of the engine and can predict when the engine needs maintenance before any problem arises for the aircrew. After every flight, the crew of an aircraft report any unusual behaviour of the aircraft to the maintenance crew so that incipient problems can be dealt with before there is any danger of breakdown.
Car owners are not this diligent
Towing
Cars are expected to break down and are designed to be towed. Aircraft are maintained so that they don't need this and the airframes are not designed to be towed in the air, there is no towing point with enough strength other than that designed into the landing-gear for gentle low-speed towing on the ground.
You cannot attach a towline to an aircraft that is not under good control, if the pilots are incapacitated or if the aircraft is damaged such that steady flight is impossible (e.g. phugoid cycles etc). If the aircraft is under good control it is probably able to fly or glide to an alternate airfield or attempt an emergency landing.
Time is of the essence
Say a 747 lost all four engines, there would probably not be enough time to launch a rescue tow-aircraft from a nearby airport and reach the plane in time to do anything useful in mid air. Particularly if the 747 is in mid-Pacific or flying through a volcanic ash-cloud. It is better to design the aircraft to cope as well as we can make it.
A car can wait an hour or two at the side of the road. An aircraft cannot wait.

Unless the pilots are incapacitated the plane could be turned to glide towards the tug. That would save some time at least.

As others have pointed out, the plane that would benefit from towing would go down before it could be reached by a tow plane.
Even if the tow plane could catch up to the glider it would be difficult to do the hookup quickly. You would need some kind of special apparatus to capture the tow hook and attach it. Doing this would be very difficult because the aircraft would be in different configurations.
For example, lets say it is two 737, one with engines out. The stall speed for a 737 is 150 knots, so it might be going, say 180 knots with a glide ratio of 15:1. At this rate it will be descending at 1200 ft/min. That is a FAST descent rate, almost crashing/out of control. For example, if you descend faster than 1000 ft/min in a flight test you will be automatically failed.
The cruising speed for the tow plane is 450 knots, so he would have to somehow slow down to 180 knots AND be descending at 1200 ft/min AND stay directly in front of the glide plane while the hookup occurred. Doing all three of these things would be very, very difficult.

That's a good point.

There are several reasons that this idea would not be practical.
An gliding aircraft flying at around 30,000ft would have, say, 20 mins before it hits the ground. If there is a suitable airfield within that range it stands a decent chance of landing safely.
The stricken aircraft would be travelling at, say, Mach 0.8 so only a fast fighter jet would be capable of chasing and catching it from behind in the available time. Any other rescue aircraft would have to approach from the front, circle and manoeuvre into position.
The time constraint makes this almost impossible. Assuming the rescue aircraft took 10 mins to prepare and take off, then the manoeuvring and attachment of the tow could add another 5 mins. That would allow only a few minutes to actually catch the stricken aircraft.
Gliders are designed to be very light aircraft and get towed up by relatively powerful tugs. They then release the tow - it is not re-attached! The airframe of a glider is designed to take the forces involved in towing; that of a passenger aircraft is not. Would it be possible to re-design all passenger planes to cope with this very unlikely scenario of total engine failure without adding weight and reducing efficiency? I doubt it.
As mentioned by David Richerby, air-to-air refuelling is currently a very expert skill practised by a handful of the best Air Force pilots. Some cunning new technology would be needed before the principle could be used on commercial aircraft.
Rather than this idea, a more useful and practical suggestion might be to add some sort of remote control function to be used in the case of the pilots becoming incapacitated or terrorists taking over the aircraft. Such technology would need to  be robustly fail-safe and many crashes have shown that that isn't easy to achieve.

Who gets to override the override?

And you don't need to apply this new technology just to any commercial aircraft -- you need it to work on commercial aircraft whose engines have failed!

This has happened under wartime conditions.
Pardo's Push Captain Bob Pardo pushed another F4 Phantom that had lost its engines into Laotian airspace after a raid on N Vietnam, to where the pilots could eject into less than hostile ground. All while Pardo's plane lost one engine due to battle damage and a fire.
Robbie Reisner pushed an F86 Sabre that had run out of fuel, out of N Korean airspace and over the ocean. Unfortunately, the pilot drowned when he ejected, landed in the ocean, and became entangled in his chute lines.
However... If you undertake a study of high profile commercial aviation incidents, you will find that almost none of them could have been mitigated with this scheme. Here's a quick spot check...
AF447 High altitude stall in the middle of the Atlantic. Went down in less than ten minutes.
JAL 123 loss of horizontal stabilizer... aircraft uncontrollable. Would have just taken the tow plane down.
USAir 427 malfunctioning rudder control unit on landing approach - no time, aircraft uncontrollable.
ValuJet 592 Fire in the cargo hold. Burned through control lines and probably incapacitated the crew.
BA 9 Lost engines due to volcanic ash. Three engines restarted. "I trust you are not in too much distress"
USAir 1549 Lost engines due to bird collision shortly after takeoff. Not enough time to do anything other than ditch.
Alaska Air 261 Vertical stabilizer jackscrew malfunctioned due to poor maintenance. Aircraft uncontrollable.
TACA Air 110 Lost engines due to storm. Landed on levee without damage by unbelievably talented pilot.
Lauda Air 004 Thrust reverser deployed inflight. Aircraft out of control. We learned that the certification that the aircraft could fly with a thrust reverser deployed was inadequate from this incident.
In all of these, only TACA 110 or BA 9 might have benefited from a tow plane, and even so, there probably wasn't enough time, as both planes could remain airborne for maybe 20-30 minutes.
So it's an interesting idea, but as of today, an airliner losing all engines is extremely rare, as contemporary gas turbines are very reliable - enough to certify crossing major oceans with only two engines. The funds for modifications for a tow hookup, the training in how to do it, and the maintenance of dedicated tow aircraft, would be better spent addressing the issues that are causing most accidents.

JL123 lost its vertical stabiliser, and AS261 lost control of its horizontal stabiliser, not vice versa.

The OP asks about towing and this has been comprehensively explored in the preceding answers.
However, we could widen the discussion by fitting the stricken aircraft with a docking mechanism on the underside. Then the rescue aircraft (with a matching docking unit on the top side) could maneuver beneath it and lock on. We would then have a composite structure like the 747-space shuttle transporter configuration. A sufficiently powerful rescue ship could then fly the pair down to a safe landing.
Further enhancements occur: (a) The docking port could have a manhole through which the PAX could be evacuated into the rescue ship. (b) A command-interface could enable the rescue pilot to control the flight surfaces on the stricken plane (assuming they were still functional), thus making it easier to fly.

Bear in mind that an empty Space Shuttle weighs 78 tonnes, whereas even a Boeing 757 full of fuel and passengers can weigh up to 125 tonnes and a 777 can be up to 350t. (And let's not get into the 590-tonne Airbus A380.)

And even then, carrying the Space Shuttle reduced the aircraft's range from 5,500 miles to 1,000 miles. Still a considerable distance, granted, but goes to show just how much that drag does! (The Shuttle Orbiter wasn't that non-aerodynamic from the front.)

There has to be consideration for whether the towing process would remain at a stable altitude, or just provide assist to the nearest airport, calling into question the amount of power that would be required to assist. Given the amount of turbulence that would be generated from the towing craft (and the bigger it is, the worse it would be) it seems unlikely the disabled aircraft would be able sustain stable flight and structural integrity.
You also need to consider the relatively small number of aircraft that become completely "disabled" without being impacted by some related catastrophic event that otherwise compromises it's flight worthiness. There are very few instances of US Air 1549 and most would be too close to the ground to allow any time to react without the famed Star Trek Tractor Beam
Perhaps with a highly specialized design process some of the challenges could be overcome, but the practicality of being able to actually have the proper assistance available would negate the feasibility.

Air-to-air refuelling shows that it's perfectly possible to have two aircraft flying in the sort of close formation that would be required for towing. On the other hand, air-to-air refuelling is a difficult manoeuvre to carry out in a fully operational plane even when the pilots do it every day; for a pilot to do it once in their career, in a plane with no engines, sounds like a very big ask.

@DavidRicherby Air to Air refueling, correct me if I'm wrong, is a well planned operation handled by experts in the field, and even then it does not involve the stresses of towing an unpowered aircraft.

@NPSF3000 You are correct. But it shows that it is possible to have two large planes flying in the same sort of close formation you would need for towing, which contradicts the claim in this answer that the towing aircraft would generate so much turbulence that the towed craft would be unable to fly.

With enough engines and all the right hardware...sure, it's possible.  See this report on tow launching an F-106: http://www.nasa.gov/centers/dryden/history/pastprojects/Eclipse/index.html
The problem is that it's just not practical.  Nevermind the actual execution of a pickup maneuver.   As mentioned in previous answers the costs of a standby fleet required to execute reliable pickups are very high.  There would be zero utilization of such a fleet.
Your edit asks about a fighter jet serving as the tow plane.  Yeah, sure, it's technically possible to build a trap of some kind to be a tow rig on an airliner.  If afterburner is required to keep both planes aloft tow time would be extremely limited though.


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Can a commerical jet fly into a tropical cyclone?
There is little doubt on whether planes can fly over a tropical cyclone as clearly demonstrated by this video of a Gulfstream jet flying over hurricane Katrina in 2005 to drop weather instruments.
I do not know the intensity of cyclonic wind at 10km above sea level, but my limited understanding on the subject suggest that the wind is strongest near the surface and weakens with height. If a small plane with high service ceiling can fly over such a powerful storm. Is it possible for a larger plane with a lower service ceiling to fly into a cyclone unscathed?
Considering that most pilots would try to go around a cyclone and that safety regulations may also forbid pilots from putting their passengers in any kind of risk that airlines do not want to bear, by just strictly looking at the aerodynamics and aeronautics of the aircraft, is it feasible for large commercial planes like 747 to fly into a tropical cyclone?

Consider the flight envelope (maximum cross wind, accelerations, ...) to see if the B747 will stay in one piece into the cyclone

The maximum lift a wing can create depends on the dynamic pressure. If the plane flies well below the speed at which maximum lift equals maximum wing root bending moment (called $v_A$), a gust will not be able to break the plane, but the ride will be very uncomfortable.

I think you mean can fly into a tropical cyclone and survive. Flying into it means nothing.

Anything can fly into a cyclone. The question is whether it will fly back out.

If the wind shear (sometimes called wind gradient, which in my opinion is the better term) encountered in that part of the cyclone the aircraft is penetrating is less than what the aircraft can handle, then, yes, an aircraft can safely fly into a cyclone.
What the aircraft can handle varies greatly depending on the speed at which it is being flown. Large aircraft have a recommended turbulence penetration speed, both in terms of knots and mach. In the absence of such a recommendation, V speeds that are relevant are Va, Vb, and Vo. http://en.wikipedia.org/wiki/V_speeds is a good V speed terminology reference.
I do not know what typical wind gradient values within a cyclone are or what their distribution within the cyclonic area is. However, I would be surprised if they were significantly greater than gradients within tropical thunderstorms, and aircraft do penetrate such.
In season there's a roughly north-south line of thunderstorms that regularly develops between Sumatra and Sri Lanka with tops greater than 50,000 feet. Lacking the fuel to go around the line, we would regularly go through it using radar to avoid the worst. However, with those old radars (back in the 1990s in 747s), it was not uncommon for us to wind up in a cell.

I suspect many a seat was browned with sudden wind shear!

@HCBPshenanigans True, but that would happen normally as these were Hadj flights out of Jakarta, and most of the pax had never been in an airplane before or, if returning them from Mecca, it was only their second time. High density seating (Indonesians are small generally) so 480 to 500 in back. With sustained heavy turbulence, most of the pax would get sick. During the 10-day break between the inbound and the outbound Hadj flights, the aircraft were taken to Singapore for fumigation and deodorizing. That was then done again at the end of the whole operation.

Interesting answer. I was hoping if someone with the experience of flying into cyclone can provide further insights :)

Fly right into a cyclone? Unlikely the plane has been tested for it, and unless the pilot was a former P-3 / C-130 Hurricane Hunter pilot (or has both balls and stomach of steel) unlikely they will try.
P-3 orion and Hercules aircraft have flown into storms many times. They weren't built especially strong other than being a standard military aircraft. A U-2 was used for hurricane research once, and that aircraft is basically flying tinfoil. I suspect it was far enough above the storm that it didn't notice.
So, and this is purely speculative, I think a 747 can take a lot more abuse than it regularly gets. But as the cost of failure is rather high I don't think anyone wants to be first (and possibly last) to try it.

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sort: votes


text:
Why does DME colocated with VOR require more separation?
In earlier versions of ICAO Doc 4444 (Amendment 9 and earlier), two aircraft were deemed to be laterally separated if they were departing a VOR on radials which diverged by at least 15 degrees and if at least one of the aircraft was at least 15 NM from the VOR.
However, as of Amendment 10, this distance requirement has increased to 17 NM (or more) if the distance measurement is based on DME:

When distance from VOR is based on co-located DME, distance of one aircraft should be at least 17 NM from VOR below FL190 and 18 NM from VOR at or above FL190.

What made ICAO change this separation?

Welcome to Aviation.SE! Can you quote the relevant section from ICAO Doc 4444?

ICAO DOC 4444 AMDT 10 LATERAL SEPARATION AND MINIMA

The request is to quote it in your question rather than expect people to look it up.

Voting to close as "unclear" until the question is clarified enough that I can understand what's being asked without needing to google-search then read a lengthy document.

As desired, I have quoted the exact text

In ICAO Doc 4444, These is no mention of co-located DME. It is mentioned as an additional note in MATS Part I (India). However the reason may be the answer given by randomhead

Ohh...is it so...then I have quoted wrong reference

The change appears to be clarifying that if the 15 NM distance determination is based on ground distance, for example the aircraft has passed a fix which is known to be farther than 15 NM from the VOR, that is acceptable. The increased minimum distance only applies when the distance is measured using DME.
This is because DME measures slant-range distance between the antenna in the aircraft and the transponder on the ground. The calculated distance is the hypotenuse of a right triangle whose other sides are the actual over-the-ground distance and the height of the aircraft above the DME transponder. This hypotenuse will by necessity be greater than the over-the-ground distance. For example, when the aircraft is 15 NM from the DME transponder and at FL190, the DME measurement will be:
$$
\begin{align}
\mathrm{DME}^2 &= x^2 + h^2 \\
    &= \left(15 \mathrm{~NM} \cdot \frac{6076 \mathrm{~ft}}{1 \mathrm{~NM}} \right)^2 + \left(19000 \mathrm{~ft} \right)^2 \\
\mathrm{DME} &= \sqrt{ 91140^2 \mathrm{~ft}^2 + 19000^2 \mathrm{~ft}^2 } \\
    &= 93100 \mathrm{~ft} \\
    &= 15.3  \mathrm{~NM}
\end{align}
$$
Whereas if the aircraft is at FL450 above the exact same spot, the DME measurement will be 16.7 NM; at FL600 the measurement will be 18.0 NM. You can see that if the intention is to ensure that an aircraft is at least 15 NM from the VOR over the ground, and if DME is used to measure that distance, you need the DME measurement to read greater than 15 NM—and the amount by which it must be greater increases as the aircraft's altitude increases.
You will also note that even at very high altitudes the required DME distance is lower than what is prescribed in Doc 4444. I would guess that ICAO wanted to add some buffer to the allowable minimum distance in the interest of safety.

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text:
What does the phrase “turnouts approved” mean?
What does the (apparently nonstandard judging by its absence in the Pilot/Controller Glossary) phrase “turnouts approved” mean when given in the context of a takeoff clearance?

Do you think what you have heard could be something like: "Left turn out's approved"? (Meaning that the pilot is cleared to turn left after departure)

@J.Hougaard I don’t recall the turn direction being part of the call, which made me wonder whether it would really be at pilot’s discretion. Glad to see an ATC specialist participating in the community!

When departing from a towered field pilots may request something other than a "standard" departure. As an example, consider the noise abatement procedures for my home field shown below:

When departing from Runway 14 the standard noise-abatement departure for light aircraft requires you to turn south (heading 190) when you pass the departure end of the runway.  This is obviously inconvenient if your destination is to the north, so you can request a northbound departure.
If the tower can accommodate your request they will clear you for the non-standard departure, usually with the phrase "left turn-out approved" or "northbound departure approved", and a heading if necessary.

I have gotten "turnout approved" on all sorts of departures, even charted noise abatement ones. Usually the tower (or ground in some airports) will ask  "say departure request" and that's when you can say "left crosswind" or "national cemetery", and get the approval.

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text:
What are the experience requirements and process for becoming an FAA Designated Pilot Examiner?
When it comes time to hire a new Designated Pilot Examiner (DPE), what does the FAA look for? What triggers new DPE job openings? How do the application and onboarding processes work? Are there more written tests? Is there a “checkride checkride”?

You can start with the FAA's reference page for Designated Pilot Examiner.
It will point you to the FAA Order 8900.2 General Aviation Airman Designee Handbook.  It's all there.  You'll need to talk to your local Flight Standards District Office (FSDO) as they are responsible for administering the program. The general eligibility requirements are:

General Eligibility Requirements. The managing office must carefully consider all of the requirements before designating an
  applicant or renewing a designee. The general requirements for
  appointment, which are reviewed by the NEB, are:

a.    Minimum Age. Minimum age of 23 years for all designees.
b.    Personality Traits. Must exhibit integrity, professionalism, and
  sound judgment.
c.    Training Requirement. Must have satisfactorily completed the
  applicable training requirement before appointment/renewal as a
  designee.
d.    Knowledge of Guidance Materials. Must have access to, and
  adequate knowledge of, the current regulations, policies, directives,
  and related guidance material appropriate to authorized functions.
e.    Command of English Language. Must be able to fluently read,
  write, speak, and understand the English language.
f.    Objectivity. Must maintain the highest degree of objectivity
  while performing authorized functions.
g.    Good Record. Must have a good record in the aviation industry.
h.    Technology Access. Must have internet access, as well as access
  to a computer and printer with hardware/software sufficient to support
  the required activities.
Note:  A designee is not required to be a U.S. citizen.
Note:  Additional eligibility requirements for specific designee types
  are included in the applicable designee type specific chapters
  (Chapters 6 and 7) of this order.

As to what the FAA is looking for (this from a DPE, I used to work with), the FAA is looking for someone they can trust to perform the job to standards. They expect a DPE candidate to be an experienced instructor.  They'll look at the the history of students signed off for check rides by that person. If any significant number of recommended students aren't passing check rides or 'just squeak by', it won't reflect favorably on the applicant.  OTOH, if the recommended students are well prepared and almost always pass, that's a good indication. That shows the instructor's standards are the same as the FAA's.
'Openings' for DPE positions are driven by supply and demand. The purpose of any Designee is to help manage the workload imposed on the FAA's office. If the office can handle the number of applicant's, they won't add a DPE. And if an existing DPE isn't performing a minimum of examinations, they'll lose the Designation. Most of the DPEs I've known worked for flight schools where there was a steady stream of students.

It is also EXTREMELY political.  Start networking now to get an opening in 5yrs.


text:
Do solo night time and “towered” landings total separately toward the solo night requirements in FAR 61.129?
FAR 61.129(a)(4)(ii) reads as follows for an applicant for commercial airplane single-engine, and makes similar provisions for other categories and classes.

(4) Ten hours of solo flight time … that include -
…
    (ii) 5 hours in night VFR conditions with 10 takeoffs and 10 landings (with each landing involving a flight in the traffic pattern) at an airport with an operating control tower.

Must a solo flight be conducted at night and involve at least one landing at an airport with an operating control tower to count, or do night time and “towered” landings total separately? Given a pilot with five hundred solo night hours all to pilot-controlled airports who goes up at night to fly ten laps around the patch at a nearby Class C, where does that pilot stand with respect to the requirement above?

501 solo night hours and 10 towered landings, or
1 solo night hour and 10 towered landings

Night time does not need to include a landing at a controlled airport to count.  You just must have at least 10 solo night landings at a controlled tower, as well as 10 hours of solo night time, they don't have to happen together (though whatever time it takes you to get those landings counts toward the 10 hours too).
The pilot in your question would have 501 solo night hours and 10 towered landings.

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text:
What is the explanation of R28///// in METAR?
In an Aviation Routine Weather Report (METAR), what is the explanation for R28///// in the RVR section? R28 stands for Runway 28 followed by visibility in meters. But still, I am curious as to why 5 forward slashes are used instead of 4?
Source:

Indira Gandhi International Airport (IGI), Delhi, India METAR report on 5th Jan, 2022 21:30IST (GMT +5:30)
VIDP 051600Z 13009KT 1500 R28///// R29/2000 RA BKN030 OVC080 13/13 Q1016 NOSIG=

From NOTAM

Q) VIDF/QFTAS/I/NBO /A /000/999/3006N07544E
A) VIDP
B) 22/01/05 14:16 C) 22/01/06 12:00
E) INSTRUMENTAL RVR OF RWY 28-TDZ NOT AVBL DUE TECHNICAL FAULT AT SITE.

From @randomhead

but my guess (from looking at the R29 RVR value) is that the first slash is part of R28/ (similar to R29/2000) and the four slashes after that replace the actual reported number.


text:
Can anyone identify this old airplane?
Can anyone identify this old airplane, and/or what era it's likely to be from? The photo is from northern Italy, and it's the only photo I have. I'd be very grateful for the help!

Are you sure this isn't some amusement park ride? Judging by the size of the blades of grass and dandelions, it's doubtful a full-size adult could sit in that thing.

It does look a lot like a Aeronca L-3. Maybe someone might have better information. https://en.wikipedia.org/wiki/Aeronca_L-3

@gwally No, it doesn't.  The L3 has a wrap-around windshield; this has a framed one.  The engine heads aren't similar, and L3 doesn't have the tiny air intake on top of the cowling.  Bottom intake is a very different shape.  Top-hinged windows are a relative rarity, they ought to be helpful here.

I've checked all planes in the Wikipedia categories 1950s/1960s U.S utility and training aircraft with no matches. Based on the shapes, I reckon that it's probably a homebuilt or kitplane.

It seems to be a single seat microlight aircraft. There are so many types and varieties of these, often home-built,  that it is difficult to determine exactly what make / model it is without more pictures.

Where in northern Italy was this photo taken?

It's from near Asti.

Reasons that it would be just a pretend airplane, perhaps the body of a wheeled vehicle:

big awkward holes on the cowl sides for headlights
paint scheme is straight lines only, inexpensive
unusual tiny duct in the top of the cowl

But it does have an antenna poking out of the roof. Molto misterioso.
If one rotated the panel below the side window half a turn about the vehicle's pitch axis, its stripes would align with the cowl's.  So it is indeed the door, not something else.
Through the gap behind the door, one sees what might be grass.  The vehicle may not have a floor back there.
Era:

cowl top's deterioration suggests fiberglass, so after 1950
paint scheme is 1960's

red light on top of the tail is not illegal, it is actually very common, see here. It is the rotating (flashing) beacon.

Cessna 150s, 152s, 172s, 182s, and who knows what others, had top-hinged windows.  Probably 120s and 140s as well.  Sometimes when renting, I would bring along needle-nosed pliers that I used to pull the pin out of the keeper on the bottom, to allow the window to open fully rather than the 6 inches or so that would otherwise be possible.  The airflow would hold the window up against the underside of the wing (except it would fall back down if you lowered the flaps at low airspeed.)  I made sure to always insert the pin back again before checking the plane back in.

(Not intending to suggest any Cessna as an actual answer here though.  Just making a point about airworthiness of top-hinged windows.)

No visible seal on the window's leading edge makes me suspicious.  But the elephant in the bedroom remains what looks like a workshop light stuck into the cowl without a plexiglas fairing (the other transparent surfaces are severely weathered), with a hint of another one on the other side.

Not to mention the door and the window don't line up at all.

What about the big awkward “stuff” (hard to see) on the underside?  That sure suggests an amusement thing to me - possibly even part of a stand-alone “kiddie” ride (like the coin op ones sometimes found outside a store).

Down there you'd expect a radiator, which the black thing might be.  But the cowl cutout offers more clearance from below than from the impinging airstream.  But but, commercial kiddie rides wouldn't bother with hinged windows and a roof antenna.  Sempre misterioso.

The appearance of what little of the engine is visible suggests a real airplane, not a (presumably unpowered) pretend airplane of some sort.  It appears that those may possibly be the tops of air-cooled cylinders barely protruding from the side holes in the cowl.
The vertical tail looks 50's-ish or newer, w/ the squared off top. Obviously the plane had a high-wing configuration with the wing atop the cabin, though only the fairing remains.
The top-hinged window doesn't seem to be a "red herring"-- for example, Cessna 150s, 152s, 172s, and 182s had top-hinged windows-- but hinged to the door, not the fuselage!  The door itself looks odd -- looking at the paint, one wonders if what appears to be the front of the door is actually the back, so that that door actually belongs on the other side of the airplane.  Or if perhaps that is actually part of the horizontal tail, rather than a door.

Yes  , rotate that door 180 degrees, and the paint stripes will line up nicely.


text:
Are 0g pushovers in a C172 safe/legal?
I see YouTube pilots do it all the time, but I’m wondering how safe this maneuver really is given the fuel is a gravity fed system. Also, is it legal?

I guess you are after the single propeller Cessnas, be cause not every Cessna has a gravity fed fuel system. The Citations are definitely not gravity fed, and I did many 0g flights in one of those. It typically would set of a master caution, because the oil system for lubricating the engines is gravity fed. The manufacturer had assured the operator that for the brief duration of the 0 g flight (~15 seconds), it would not be a problem.

When doing "bunts", it's about the oil, not the fuel. The airframe doesn't care; it's in a ballistic arc and is completely unloaded, like some trash you launched into a neighbor's yard with your Yard-A-Pult.
Overall, the main risk is of a temporary drop in engine oil pressure when oil in the sump turns to globs and floats around, potentially unporting the oil pump suction pickup at the bottom of the sump.
The effects of this are less severe in a carbureted engine because the engine will also quit temporarily while this is happening (the carb will flood), and without the torque related forces acting on the main bearings, it's unlikely to do damage to the main bearings for the couple of seconds you can sustain the bunt.
Oil pressure loss is more likely to happen if you push too hard and go negative G. All the garbage that was on the floor, and is now on the ceiling of the cabin, also tells you that the oil in the engine is up against the top of the sump and running backwards through the drain path into the main crankcase, and the oil pickup is sucking air for sure.
If the engine is fuel injected, the risk of doing real bearing damage is higher; it'll still produce power during the time you can sustain the maneuver (until fuel in the lines is consumed if the fuel in the tanks unports, which will take longer than you can sustain the bunt) and if the oil pressure drops while it's making power, that's a very bad thing, as it's likely the main bearings will achieve metal to metal contact, and it's downhill from there.
If I was an FBO who learned that my renters were doing zero G bunts in my planes, I'd probably be not too happy about it.


text:
Can a missed approach be used to satisfy the requirements for the long cross country as part of an instrument rating?
The long cross country requirements are as follows:

§61.65(d)(2)
(ii) Instrument flight training on cross country flight procedures, including one cross country flight in an airplane with an authorized instructor, that is performed under instrument flight rules, when a flight plan has been filed with an air traffic control facility, and that involves -
(A) A flight of 250 nautical miles along airways or by directed routing from an air traffic control facility;
(B) An instrument approach at each airport; and
(C) Three different kinds of approaches with the use of navigation
systems.

I flew from my base airport, a 100nm leg, performed an RNAV approach to land, departed on another 100nm leg, performed an ILS approach to land, departed on the last 100nm leg back to my base airport. There, while I flew the VOR approach past the FAF, we decided to go missed due to terrible wind gusts. We diverted VFR to a nearby airport and proceeded to land there.
Have I actually satisfied the requirements in §61.65(d)(2)(ii)(B) and (C)?

I vaguely recall reading (either here or on Reddit) about an interpretation that said something to the effect of: if you're in IMC past the FAF, you can go missed any time past the FAF and log the approach. If you're in VMC, you need to take the approach all the way to the DH/MDA/whatever in order to log the approach. Could be misremembering.

It was simulated instrument, but not actual IMC. Do you suppose that counts as IFR in VMC or IFR in IMC?

A poor example, but anyway: my first solo was cut short due to adverse weather closing in on the airport. I did not fly the "required" amount of touch and gos, but as everything else went smoothly, it was deemed a good performance as I appropriately used my judgement. I actually do not remember (and am too lazy to check) whether there are strict guidelines for the stuff one must do on a first solo...

I don't see why it wouldn't count since you were passed the final approach fix. You would have switched to visuals once you have had the runway in sight.

Have you satisfied §61.65(d)(2)(ii)?
Yes.
I also looked to see that you made a landing at an airport beyond 50NM from the original point of departure.  It sounds like you did so it is a cross country flight.
The flight was conducted under IFR and coordination with ATC was necessary to conduct the missed approach and then cancel IFR and fly visually to the alternate.  An examiner, when looking at the logbooks, may ask you questions about that flight.  As long as you are forthright with the conditions of the flight should be no problem.

I would also suggest you ask the examiner you intend to administer your checkride.  If he is ok with it, then go for it.  After you're awarded the rating nobody is going to query whether you had satisfied the requirements of §61.65(d)(2)(ii).


text:
How is separation ensured after a go-around due to a busy runway
In watching aviation / ATC videos, I've often seen situations like the following: airplane A is coming in to land, but airplane B is already on the same runway trying to take off. Either it's slow taking off, or the controller did not provide enough separation, or for whatever reason the pilot of airplane A is not comfortable with this situation, so airplane A executes a go-around.
At the moment this happens, both planes are presumably moving exactly along the direction of the runway, plane B being slow (just taking off) and plane A being fast (doing a go-around).  So presumably plane A will at some point overtake plane B, making the horizontal separation between them zero. Both airplanes are climbing. How is vertical separation between them ensured?
Or does the going-around plane turn right away? In which case, isn't there a problem with a possible stall? Also is the turn heading somehow pre-determined in advance (because I'd imagine there wouldn't be time to ask the controller in a go-around situation)?

It depends on... so many circumstances. You have regulation and procedures for almost each classic airport. You have trained pilots, ie, go-arounds are "professionally performed with separation" in the first place, you don't go-around too late. For similar aircraft, departing ones are heavy, arriving ones are light (burnt fuel), a go around has an higher climb rate than a taking-off plane, separation includes vertical. Yes, conflicts do happen, ranting pilots aswell (on radio), but actual close calls are extremely rare for airliners. General aviation side at uncontrolled airfields however...

Interesting coincidence: Kelsey from the 74 Gear channel just alluded to this in https://youtu.be/sXY2gFn6cI0. He discusses a situation where a controller tries to squeeze a departing aircraft in between two landing aircraft, the second aircraft goes around, and then the controller gets angry. He then recounts a similar situation where he chose to land instead of going around precisely because of the  potential conflict you are asking about.

A note for you, @Jörg: I wasn't there and I don't know the details of how JFK works, but if the controller says "it would have been tight but it would have worked" I would tend to believe that. One very important piece of information is that it IS legal to have two aircraft over the runway at the same time, depending on certain details, and the controller was almost certainly planning on using that rule to the fullest.

There are a lot of different ways this can play out, and the details matter. I will be answering in the context of faa-regulations.
One point before I go further is that visual separation is a thing, and a very common thing in the usa at least. This can be tower-applied visual separation, where the controller has the aircraft in sight and issues instructions to ensure they don't conflict, or pilot-applied visual separation, where one pilot has the other in sight and maneuvers as necessary to avoid a conflict. In either case separation is allowed to reduce below the "standard" separation requirements.
In situations where visual separation cannot be used, the general rule is that aircraft need to be three miles apart. But this is allowed to reduce to only two miles if one is departing and the other is arriving, provided separation will increase to three miles within one minute after departure. This two-mile minimum must exist at the time the aircraft on the runway begins its takeoff roll.
Even in situations where visual separation can be used there are still minimum distance rules between an arrival and a departure using the same runway—these minimums can't be replaced by visual separation. Legal separation can be as low as 1.0, 0.75, or even 0.5 miles depending on the weight and engine configuration of the aircraft involved (using weight and configuration as a proxy for speed).
My point with the above is that your presumption

plane A will at some point overtake plane B, making the horizontal separation between them zero

does not really hold true in the majority of situations. Very occasionally a controller will make a bad blunder and it can happen, as shown in this recent video. In a case like that it's a lot hairier and the controller should be on top of the situation issuing traffic calls and vectors to pry the airplanes apart. As can be seen, if the controller is slow to react an onboard system called TCAS will alert the pilots to the impending collision and will issue instructions which override ATC instructions. All airliners and many larger business jets have TCAS these days.
But most of the time the controller will act much sooner—the video above is really the exception which proves the rule. Standard separation has quite a lot of buffer built in; if the controller does suffer a loss of separation there is still plenty of time to rectify the situation and prevent a collision. Even if it takes a few seconds for them to react it's almost never the case that the aircraft going around will catch up to the aircraft departing, provided the two aircraft are of similar performance classes.

As for actual methods to prevent a collision:

The classic is to instruct the go-around to "offset left/right of the runway." This isn't a standard instruction found in the controller rulebook but it is a very common one "in the field," especially at towers which work a lot of aircraft in the VFR pattern; of course this is a bad idea if the weather is bad and the pilots can't see any obstructions near them. This instruction all but guarantees the aircraft won't hit, provided the go-around offsets to the opposite side relative to where the departure is turning.
If an offset isn't possible the controller can issue turns to avoid conflict; the go-around turns away from the departure and vice-versa. Again this can less effective in bad visibility because pilots will need to gain altitude before being comfortable turning away from the obstacle-free area along the runway centerline. (There are published missed approach procedures but in most cases ATC will issue a vector instead of allowing the published missed, which likely won't provide the immediate separation they need and often conflicts with other streams of aircraft too.)
The go-around can be issued a climb to above the altitude the departure is climbing to, and/or the departure can be stopped at a lower altitude than they were issued initially. Most of the time they'll need to keep climbing very soon in order to avoid obstacles or terrain on the ground, but a short level-off is better than being run over by the go-around...


text:
How precise are altimeters?
How precise and how accurate are typical altimeters these days? That is, if two planes are flying (side-by-side, very near each other), and both altimeters show the same Flight Level, what is the maximum vertical difference in actual altitude you would expect to see between them? (I.e. is it on the order of a few meters, a few tens of meters, etc?) Is there any legal standard for precision/accuracy of the altimeter that must be met (let's say in the US)?

While Accuracy and Precision are closely related, they're not the same thing.
In the context of your question both are important:
Accuracy
In the US altimeters are broadly required to comply with FAR 43 Appendix E limits for accuracy (technically this is regulatory for IFR flight, but TSO'd "sensitive altimeters" will generally meet these requirements - at least when they left the factory - and that's what you're going to find in most aircraft).
The accuracy requirements provided in FAR 43 are based on mechanical altimeters, and are subject to a number of requirements (friction error limits, hysterisis limits, etc.), but the test tables there are a good guide to the accuracy of "typical" altimeters.
Also note that the accuracy of sensitive altimeters depends on the pressure setting the pilot enters (an incorrect pressure setting could mean substantial error). In "the flight levels" everyone uses the same standard altimeter setting (29.92 inches of mercury / 1013 millibars) to avoid this issue (similarly the ATC transponder transmits an altitude assuming a pressure of 29.92 inches of mercury - ATC's computers correct that value based on local altimeter settings as required).

Depending on the design digital altimeters may also be immune to some of the accuracy-affecting issues in an analog/mechanical altimeter - for example a solid-state digital altimeter should not suffer from "friction error" as there's no rotating/moving shaft involved.

Precision
Analog altimeters are "reasonably precise" -- take this example:

The tick marks are every 20 feet. One could easily eyeball 20 foot increments, and even 10 foot increments (with the pointer directly between two ticks). Similarly the pressure settings are marked every 0.02 inches of mercury (or 1mb), allowing for a fairly precise setting of the value.
Digital altimeters are extremely precise (often offering one-foot precision in their display, and 0.01 inches of mercury for the pressure setting).

I believe the precision requirements for altimeter markings are specified in the relevant TSOs, but I don't have those documents handy.

In both cases the precision of the markings can exceed the accuracy of the device: At 10,000 feet the FARs allow an 80 foot tolerance, and whether your measurement is presented as a needle position (roughly to the nearest 10 feet) or a number (to the nearest foot) you could still be 79 feet higher or lower than you "think" you are and be "within tolerance".
So, combining all of this together - If we have two aircraft flying along indicating the same altitude (say 10,000 feet) and both altimeters are perfect there will be zero feet of vertical separation between them (the static ports of each aircraft will be at the exact same altitude).
On the other hand if both aircraft are at the outer edge of tolerance (one +80ft, one -80ft) there will be 160 feet of vertical separation between them (discounting visual "slop" in the analog altimeter and assuming the pointer is perfectly on the line and the pressure setting is perfectly dialed in).
(In either case the answer would be "WAY TOO CLOSE!")

Just to amplify something that's implied in here, "accurate" means "the value displayed is close to the true value", whereas "precise" means something similar to "the value is displayed with lots of decimal places." Thus, it is accurate (but not precise) to say that the height of Everest is 30,000ft; it is precise (but not accurate) to say that the height of Everest is 17,382ft.

"there will be 160 feet of vertical separation between them" ... well, there will be 160 feet of vertical separation between the altimeters. There will probably be a lot less between the metal! :)

David, not quite. Precise means that the variance of the displayed value from the same observation is low. So an altimeter at 1000 ft that records (992 1003 1007  990 1001) is accurate but not very precise, whereas one that measures (1009 1010 1010 1010 1011) is not accurate but more precise.

@egid yes - again if we want to get technical "The static ports of the aircraft will be 160 feet apart." -- that's probably close enough for metal to meet (especially with some taller aircraft).

Gah, that's actually what I first thought. Then I wrote something else!

Just to summarize, part 43, appendix E allows up to 20 foot error up to 1000', 80' error at 10,000', and up to 280' error at 50,000'. There are other requirements such as hysteresis and leakage.

Well, it depends a little bit on how you define accuracy. Working altimeters are as accurate as the pilot makes them. In perfect use, they work great, in typical use, they work a little less great, but still pretty well.
First of all, the altimeter is part of the pitot-static system, so that means they are dependent on having smooth airflow, and the pitot-static system being working (not clogged).
Second, altimeters in GA airplanes, not sure about others, require you to manually set the pressure of the atmosphere (barometric pressure), to get the correct reading. This can be done with some accuracy, but usually never 100%.
Finally, altimeters in GA airplanes are required to be read in a similar manner to an analog clock. So there is a little pilot error to consider.

Note though, that the question says "show same flight level", which means the altimeters are set to standard pressure and setting should not play role (in USA the transition altitude is always 18000, but in other places it may be as low as 5000 in sectors where there is no significant high ground around).

@JanHudec It's possible the OP used "flight level" in a casual sense to simply mean "altitude" without implying standard pressure. He may not know what a true "flight level" means. I've heard that term used casually and improperly quite often, especially in the recreational flight simulator world.